An internal combustion engine such as an automobile includes an electronically controlled fuel injection device for efficiently operating an internal combustion engine by appropriately adjusting the amount of air and fuel flowing into the internal combustion engine. The electronically controlled fuel injection device is provided with a flow rate sensor device for measuring a flow rate of the air flowing into the internal combustion engine.
The flow rate sensor device has a structure in which a flow rate sensor and a semiconductor element for control are mounted on a circuit board, and a semiconductor element is disposed in a space of a housing formed by a lower case and an upper cover. The flow rate sensor is exposed from the housing and is connected to the semiconductor element by wiring. The circuit board is fixed to the housing with an adhesive.
In the structure in which the circuit board is adhered to the housing, it takes time for applying and curing processes of the adhesive, and a throughput is lowered.
A rotary resistor is known which integrates a circuit board and a resin by insert molding. This rotary resistance is manufactured by the following method.
A ring-shaped O-ring is disposed on a circuit board, and the O-ring is pressed against the circuit board by a cylindrical core pin having a columnar hollow portion. To press the O-ring against the circuit board, a holding pin is slidably provided in the hollow portion of the core pin, the O-ring is fitted into the holding pin, the holding pin is projected from a tip of the core pin by energizing force of a spring, and the fitted O-ring is pressed against the circuit board. The O-ring is formed in a ring shape whose outer diameter is slightly larger than the core pin, and only the inner peripheral side is compressed by the core pin by leaving a part of the outer peripheral side of the O-ring. In this state, the resin is injected to the outer peripheral side of the core pin, and front and rear surfaces of the circuit board on the outer peripheral side of the core pin including the outer peripheral side from the core pin of the O-ring, are covered with resin. Then, the core pin is drawn out, and a rotating member is attached to the columnar space on the circuit board on which the core pin has been disposed. A lid as a holding member is attached to an upper surface of the rotating member. According to this structure, since the circuit board and the resin are integrated by insert molding, a throughput is improved. In addition, it is described that, since a gap between the rotating member and the circuit board is sealed by the O-ring, it is suppressed that the resin protrudes the upper surface side of the circuit board, and a resin burr is formed (for example, refer to PTL 1).